It is known from U.S. Pat. No. 4,020,233 to form cured polythioethers by admixing the composition comprising an ethylenically unsaturated compound containing at least two unsaturated carbon-to-carbon bonds per molecule, a polythiol containing at least two thiol groups per molecule, a photoinitiator and a catalytic amount of a pinacol and, thereafter, subjecting the admixture to UV radiation and heat. It is also known from U.S. Pat. No. 3,652,733 to form cured polythioether products from a composition comprising a polymerizable plasticizer having an average of 2-5 carbon-to-carbon unsaturated groups per molecule, a thermoplastic polymer selected from the group consisting of polyvinyl chloride and copolymers of vinyl chloride with vinyl acetate, a polythiol, and a photoinitiator by exposing said composition to UV radiation after fluxing the thermoplastic polymer at temperatures between 100.degree. and 200.degree. C. The polythiol is a necessary ingredient to assure that the plasticizer is completely cured and thus does not exude from the product. It is further known from U.S. Pat. No. 4,309,331 to form photosensitive dispersions of acrylic resins in combination with a non-volatile ethylenically unsaturated compound and a photoinitiator. It is also known from U.S. Pat. No. 4,288,527 to UV and heat cure in seriatim compositions of unsaturated acrylic or methacrylic monomers or prepolymers in combination with a photoinitiator and a substituted or unsubstituted pinacol. Further, it is known from British Patent Application 2,046,269A to photopolymerize a composition of an epoxidic prepolymer and a vinyl chloride dispersion polymer in the presence of specific photoinitiators which decompose on exposure to electromagnetic radiation. It is also known from U.S. Pat. No. 3,840,448 to cure acrylate compositions in an inert atmosphere to obtain skin cures. Further, U.S. Pat. No. 3,989,610 teaches a composition consisting of (1) a photopolymerizable, unsaturated compound containing at least two terminal ethylene groups, (2) a photosensitizer for (1), (3) an epoxy containing at least two epoxy groups and (4) a thermal initiator for the epoxy compound. The curing process involves UV curing of the photopolymerizable unsaturated compound followed by heat curing of the epoxy compound.
One object of the instant invention is to produce a composition which can be dual UV and heat cured. Another object of this invention is to produce cured products by exposing the composition to UV radiation under atmospheric conditions followed by the application of heat. Still another object is to produce a composition which, when applied to an irregular surface containing shadow areas inaccessible to UV radiation, will cure in these areas during the heat cure. Yet another object of the invention is to produce a composition which on exposure to UV radiation under atmospheric conditions will skin-cure sufficiently to maintain the composition in situ, e.g., without any runoff or sag so that the composition is properly positioned for the heat cure which follows. Other objects will become apparent from a reading hereinafter.